The present invention relates to a probe, for measuring the dimensions of objects, of the type used in conjunction with a machine which has coordinate positioning such as a coordinate measurement machine, machine tool, robotic device, or the like.
Traditionally one type of dimensional measurement probe produces a trigger signal when a contact stylus touches an object, the trigger signal causing a recording of the coordinates of the coordinate positioning machine to which the probe is attached. Sensors in the probe detect minute loadings on the stylus as the probe moves closer to the object in order to detect contact between the stylus and the object. For practical reasons the contact stylus is usually an elongate stem with an enlarged end so that it can reach features of the object to be dimensionally measured.
The stem of the stylus is not completely stiff because it is relatively slender so as to reach as many features of the object as possible. Therefore, the stylus stem will bend slightly when subjected to side loading resulting from object contact perpendicular or oblique to the axis stem, but it will not bend significantly when subjected to loading caused by contact in a direction substantially along the axis of the stem. Bending of the stylus support structure occurs also. Again the bending is greater when the stylus is loaded from the side when compared to its bending resulting from loads along the axis of the stylus.
The result of this bending causes a trigger signal which is dependent on the relative positions of the object surface and the axis of the stylus stem. In other words an object may appear to be a different size depending on the inclination of the stylus stem relative to the object's surface, caused predominantly by stylus bending and to a lesser extent by bending of the stylus support structure.